Question

Describe the "end-replication problem" in eukaryotes. How is it resolved?

Short answer

Answer: Telomerase is a specialized enzyme found in eukaryotic cells that can resolve the end-replication problem by extending the telomeres. It contains its own RNA template and uses this template to synthesize the repetitive DNA sequences of the telomeres. By extending the telomeric region, telomerase provides more space for the lagging strand synthesis to take place, thus preventing the loss of vital genetic information during DNA replication.

Step-by-step solution

Background on DNA replication

DNA replication in eukaryotic cells is a complex process involving the unwinding of the DNA double helix and using each strand as a template to synthesize a new complementary strand. The enzyme DNA polymerase III adds nucleotides to the new strand in a 5' to 3' direction.

The end-replication problem

The end-replication problem arises because DNA polymerase III can only synthesize DNA in the 5' to 3' direction. This creates a situation where leading strand replication can continue uninterrupted until the chromosome end, while the lagging strand replication leaves small gaps on the 3' end. These gaps result from the removal of RNA primers, which are necessary for initiating DNA synthesis on the lagging strand. Eventually, after multiple rounds of replication, this loss of genetic material leads to shorter chromosomes.

Role of telomeres

Telomeres are repetitive nucleotide sequences located at the ends of chromosomes that protect the chromosomes from degradation and loss of vital genetic information. They also prevent chromosomes from fusing with one another, which could cause genomic instability and other problems.

The role of telomerase

Telomerase is a specialized enzyme found in eukaryotic cells that can resolve the end-replication problem. It contains its own RNA template and uses this template to synthesize the repetitive DNA sequences of the telomeres. By extending the telomeric region, telomerase provides more space for the lagging strand synthesis to take place, thus preventing the loss of vital genetic information during DNA replication.

Overall resolution of the end-replication problem

In summary, the end-replication problem in eukaryotes is resolved by the presence of telomeres and the activity of the enzyme telomerase. Telomeres protect the chromosome ends from degradation, and telomerase replenishes the lost nucleotides during replication, ensuring the stability and integrity of the genetic material in eukaryotic cells.